1. Field of the Invention
The present invention relates to a combination lens in which a plurality of lenses are housed in a lens barrel, and to a method for manufacturing this combination lens.
2. Description of the Related Art
With a combination lens in which a plurality of lenses are housed in a lens barrel, the spacing between the lenses needs to be maintained at high precision, and various structures have been proposed to this end. For instance, a structure has been proposed in which a plurality of spherical bodies are sandwiched between the lenses to maintain the lens spacing at high precision.
In JP H9-318858A, as shown in FIGS. 10 and 11, a plurality of concavities 101a are formed in the inner periphery of a lens frame 101, steel balls 102 are disposed in these concavities 101a for positioning, and the steel balls 102 are sandwiched between the opposing faces of lenses 103 and 104, thereby maintaining the spacing between the lenses at a predetermined distance.
Similarly, in JP H9-318859A, as shown in FIGS. 12 and 13, steel balls 112 are disposed in concavities 111a for positioning that are formed in the inner periphery of a lens frame 111, and the steel balls 112 are sandwiched between the opposing faces of lenses 113 and 114, thereby maintaining the spacing between the lenses at a predetermined distance.
Nevertheless, JP H9-318858A and JP H9-318859A require that the concavities be made sufficiently large so that they can easily accommodate the steel balls. Consequently, the positioning precision of the steel balls is not always good, and the lenses are sometimes fixed while the steel balls are still out of position, which can lead to a tilt between the lenses, deviation of the optical axis, and so forth.
Also, a plurality of steps or flanges must be formed around the inner periphery of the lens frame, but it is not easy to maintain the machining precision of the lens frame, and this can lead to a tilt between the lenses, deviation of the optical axis, and such problems, and also makes it harder to lower cost.
Furthermore, the smaller is the lens diameter, the smaller the lens frame has to be made, and it has been difficult to produce and assemble such lens frames.